The present invention relates generally to compressors and more particularly, but not exclusively, to centrifugal gas compressors.
Centrifugal gas compressors are known to have problems with noise believed to originate from the airfoils of the impellers. Many such compressors will have at least one rotating radial impeller mounted within a rigid casing and will further include an inlet pipe and inlet plenum and discharge pipe and a discharge plenum. The rapid rotation of the blades of the impeller causes them to set up some harmful pressure pulsations inside the working fluid. These pulsations can be transmitted through the discharge pipe, or other components of the compressor, resulting in potential mechanical damage or environmental noise.
It is believed that the space-varying pressure field surrounding each of the airfoils of the impeller is acting as a source of noise. This noise is due to the rapid rotation of the airfoils inside the pressurized casing of a typical gas compressor. The pressure field of each airfoil may interact with other components, such as diffuser vanes. Similarly, the pressure field of each airfoil may interact with the geometry of the collector plenum itself. In both such scenarios, pressure pulsations are developing inside the collector plenum at approximately the so-called blade passing frequency. The blade passing frequency is approximately equal to rotation speed of the impeller in rotations per second times the number of impeller blades. These pulsations are potentially of a high enough level to cause mechanical or environmental concerns. Consequently, significant efforts have focused on developing mechanisms to minimize pressure pulsations within compressors.
Heretofore, there has been a need for compressors having improved noise characteristics when considered in view of other characteristics such as unit cost, ease of design, and other competing tensions.